Mixing act as category & as forum
 

I have a particular forum that I basically want to turn into simply a container for subforums, so I never want it to contain posts/threads itself. Let me give an example to better illustrate what I'm doing. Here's a sample forum structure below:

Forum Homepage
- Cat1
-- Forum 1
-- Forum 2
- Cat2
-- Forum 3
--- Cat3
---- Forum 4
---- Forum 5
-- Forum 6

So, in my case, I'd like Forum 3 to show on the homepage like any other forum, but when you click on it, it should not try to show threads or give the option to post in it. I know I can change the Forum 3 permissions to achieve this, but I do not want any of Forum 3's subforums to inherit those permissions (users should be able to post in them like normal). Is there a way to change Forum 3's permissions so that none of its subforums inherit the changes?